Sample-and-hold (S-H) circuitry is useful as a component in such devices as analog signal filters and analog-to-digital (A/D) converters. Such devices entail overall circuitry designs having rather high accuracy--i.e., high circuitry linearity. For example, an A/D converter having an output accuracy of 10 bits (i.e., an output representing a binary digital number having 10 bit-places) requires an A/D conversion linearity of one part per 2.sup.10, that is to say, an accuracy of approximately one part per thousand. Such an accuracy translates into a distortion in the output amplitude equal to less than 60 dB. Hence the S-H circuitry contained in the A/D converter likewise must have less than 60 dB distortion. In other words, the S-H circuitry must have an accuracy of at least one part per thousand (i.e., an accuracy of at least 10 bits).
A paper by P. Vorenkamp and J. P. M. Verdaasdonk, "Fully Bipolar 120-Msample/s 10-b Track-and Hold Circuit," IEEE J. Solid-State Circuits, vol. SC-27, pp. 987-992 (July 1992), teaches S-H circuitry built in bipolar transistor technology with the following reported parameters to achieve an accuracy of 10-bits (at a 120 MHz sampling rate): a voltage supply of 5 V, a power dissipation of 40 mW, and a differential voltage swing of 1 V on a pair of balanced inputs and outputs (using a balanced, unity gain configuration). Because of the inherent base-emitter voltage drop of bipolar transistors (typically a drop of approximately 0.8 V in the ON state of such transistors), if such circuitry would be powered by a desirably lower voltage supply of 3.3 V, the circuitry could attain only an accuracy of only 6 bits. Therefore, it would be desirable to have S-H circuitry in bipolar transistor technology that can attain an accuracy of 10-bits with a voltage supply of only 3.3 V, preferably with a power dissipation lower than 40 mW, and with a larger balanced differential swing than 1 V (0.5 V single-ended).